It is well known in the construction and building industry that concrete structures require reinforcement means during the formation of the structures. Such reinforcement means typically are steel reinforcing bars or rods commonly known as "rebar".
The general procedure followed for forming a concrete foundation support structure such as a concrete pier involves drilling or excavating a shaft or hole in the ground at a predetermined location. A reinforcement cage is formed from reinforcing steel and is inserted into the drilled or excavated shaft. The reinforcement cage typically is fabricated above ground from a series of elongated steel rebar rods or similar reinforcement materials. The steel rods are usually arranged in a substantially parallel cylindrical array and are bound together in this configuration by laterally oriented rebar ties and tied thereto with conventional tie-wire.
Another configuration of the laterally extending rebar ties is an elongated section of rebar that is wound about the parallel steel rods in a helical configuration. The ties are connected to the reinforcement cage at points of contact between the parallel rods and the rebar ties by tie-wire. The rebar ties hold the parallel rods in an elongated cylindrical cage configuration. The assembled steel reinforcement cage is lowered into the drilled or excavated shaft prior to the pouting of concrete therein.
As the concrete is poured, it is desirable that the lower ends of the vertical rods of the reinforcement cage be properly supported and spaced for clearance from the bottom of the drilled or excavated shaft. A problem faced by drilled shaft contractors is trying to insert the rebar cage into a drilled or excavated shaft and maintaining the proper clearances between the cage and the side and bottom surfaces of the shaft, and also to properly support the lower ends of the vertical rods of the cage on the bottom of the drilled or excavated earthen shaft. Once the cage has been inserted into the shaft, concrete is poured about the cage to form the foundation structure.
In order to solve this problem of maintaining the vertical bar reinforcement cage in a supported and spaced clearance position in relationship to the bottom of the drilled or excavated earthen shaft space, contractors have suspended the entire cage of bar reinforcement within the drilled or excavated shaft as the concrete is poured. It is also common practice among drilled shaft foundation contractors to attach spacers to the lower ends of the vertical bars so that the bars will rest on the spacers. The spacers engage the bottom surface of the drilled or excavation shaft and prevent the reinforcement cages from coming into contact with the earthen surface and support the bar reinforcement steel cage at the same time.
There are two types of prior art spacers known to the inventor that have been utilized as spacing and support devices for concrete foundation cages. These spacers usually are installed on reinforcement cages at the building site. The first type of spacer generally used is a simple solid concrete or cementitious block that is formed in the field from waste concrete or formed from concrete purchased from a materials supply company. These solid concrete spacers typically are square or rectangular shaped and may or may not have tie-wires imbedded in them. The cementitious block spacers formed in the field are the ones that usually have the wires imbedded in them. The cast-in-field blocks generally must cure for a period of 28 days in order to obtain their designed structural strength. The ties imbedded within the cementitious monolith may be rusty which may spread to the bar reinforcement like a cancer, and the fabricated block usually is tied to the ends of the bar reinforcement by skilled ironworkers.
It is difficult and time consuming to tie or otherwise fasten the cementitious blocks to the ends of the vertical bar reinforcement and have the blocks be kept in place on the end of the bar for placement in the shaft without the blocks dangling loosely from the ends of the vertical bar during the placement of the fabricated cage in the shaft. Another problem with the cast-in-field cementitious blocks is that the concrete is generally not cured sufficiently or monitored for strength prior to the cage of steel reinforcement being lowered into the shaft, and the blocks sometimes are brittle and the weight of the bar reinforcement steel cage cracks the blocks.
The cementitious blocks purchased from a material supply company usually are low psi strength blocks, unreinforced and brittle. The purchased blocks are attached to the ends of the vertical bar reinforcement again by skilled ironworkers in a similar fashion as referenced in the cast-in-field application of spacer blocks. Similar drawbacks generally apply in the use of the purchased cementitious blocks as with the cast-in-field blocks. Both type blocks tend to break when a weight such as that of a cage of fabricated bar reinforcing steel is placed upon it because the weight of the cage of steel is concentrated on the longitudinal bars and spread over a small surface area at the ends of the bars.
Another prior art support for a rebar cage is a prefabricated cementitious solid block with imbedded wires known as the "pier bolster" and manufactured by Pieresearch of Arlington, Tex. This product is designed and produced in generally the same fashion as the concrete blocks that are cast in the field as referenced above, and are tied to the ends of the bar reinforcement in about the same fashion as those blocks cast in the field. The pier bolster blocks are tied to the lower ends of the steel reinforcing bars utilizing skilled ironworkers and the blocks usually are not secure about the ends of the bars when tied. The pier bolster usually is left dangling from the bottom ends of the reinforcing bars just like the cast-in-field blocks and the purchased cementitious blocks as described above. When the cage is set there is no guarantee that the blocks remain in true position underneath the steel reinforcement, and the blocks could possibly fall off the cage during placement. Another problem that exists in the utilization of the pier bolster is the weight of the block. The pier bolster blocks known to this inventor weigh approximately two pounds and require two men to fasten the block to the rebar cage when the cage is suspended over the shaft.
Most construction sites usually present muddy and wet conditions during the stage of foundation construction. By placing the steel reinforcing cage upon the blocks and fastening them to the ends of the reinforcing steel prior to placement sometimes causes the blocks to become contaminated with mud, etc. prior to placement in the shaft and the blocks require cleaning prior to placement. If placed into the shaft unclean, the concrete poured into the shaft to form the foundation tends to not properly bond to the contaminated surfaces.
Another problem with the pier bolster is the shelf life of the unit when not used. The concrete usually is not a problem during storage, but the tie wires embedded into the concrete monolith are likely to rust in a short period of time due to the typical corrosive environment and atmosphere that the units usually are stored in. Once the wires have rusted, some engineers will not allow the rusted or contaminated wires to contaminate the steel reinforcement. If the rusting is severe enough, then the wires may break during the fastening process. Galvanization and epoxy coatings have been used to prevent or slow the corrosive rusting process, but the galvanizing and epoxy coating processes are expensive and add more cost to the final product.
Another prior art design does not relate to the support of bar reinforcement within a concrete foundation, but is related to the fastening of a cap over the ends of bar reinforcement. The steel reinforcement bars (rebar) are usually sheared during fabrication which leaves sharp and irregular ends that can cut or cause serious injury if accidental contact happens. There are several types of plastic caps that have been placed over the ends of the bars for safety purposes. These caps usually are bright colored, orange or yellow, plastic cap devices placed over the upper exposed ends of exposed and protruding steel bars after a portion of the bars have been partially encapsulated in concrete and prior to a second pour. The bright colored plastic caps are placed onto the exposed top ends of the bars and the caps provide a smooth rounded surface about the ends of the steel reinforcement bars.
The plastic caps are secured about the reinforcing steel with flexible plastic flaps inside the cup part of the cap which bind against the bar reinforcement steel to hold it in place during use, but the flaps are also flexible enough for removal and subsequent reuse of the caps. These plastic caps are not universal and are not designed to provide an engineered structural product for construction. These caps are for safety only and are not designed to withstand and support the immense structural compressive forces imposed by the bar reinforcement cage.
Accordingly, it can be seen that it would be desirable to provide steel reinforcement rebar cages for concrete structures with spacers at the lower ends of the vertical bars which maintain space between the bars and the bottom surface of a drilled or excavated shaft. Further, it would be desirable to provide a spacer support which will retain an indefinite shelf life during storage and handling; and which is engineered structurally sound and sufficient to provide the necessary support for the rebar cage, and which is lightweight and which locks onto the end of the bar reinforcement rod, utilizing minimal unskilled labor and provides a specified spacing clearance separating and protecting the lower end of the rod from the earthen surfaces of a drilled or excavated shaft.